1912.] natural sciences of philadelphia. 453 



Summary. 



From the observations briefly outlined in this paper, it is believed 

 that we can draw the following conclusions concerning the geological 

 history of this area in central New York: (1) During Hamilton 

 time a considerable surface of the sea-bottom shallowed, this shallow- 

 ing being accompanied by the introduction of clear ocean currents 

 with the resultant cessation or at least interruption of mud deposition. 



(2) These physical changes of sea-bottom and of sea produced 

 conditions favorable to the growth and development of the same 

 coral fauna throughout the greater part of the area. The coral 

 growths varied greatly in thickness with the locality. In places 

 they endured for a considerable time, while in other nearby situations 

 the growth was discontinuous and the history is recorded in the 

 strata by thin interbedded coral bands and limy shales — the probable 

 records of old channels. 



(3) Though these changes, physical and faunal, were of short 

 duration when compared with the whole of Hamilton time, they 

 nevertheless represent perhaps the most striking episode in the 

 history of the Hamilton Sea in this area, namely, a transitory return 

 to Onondaga-like conditions, followed again by the mud-bearing 

 waters and the mud-loving fauna of the typical Hamilton. 



Among the unsolved problems connected with these reefs perhaps 

 of most importance are the following: 



(a) Correlation with coral-bearing horizons in the western portion 

 of the State. 



(6) Determination of the direction from which the faunal and 

 environmental invasion came. 



(c) Possible correlation with some important, though perhaps 

 distant, crustal movement. 



Acknowledgments are due to Mr. Sedgwick Smith, of Harvard 

 University, for assistance in the field, and to Mrs. Ethel Ostrander 

 Smith, who photographed the reef structures under rather difficult 

 conditions. 



Explanation of Plates X and XI. 



Plate X. — Coral layers fanning away from the northern margin of the Southern 

 Reef (see text figure, S) near Staghorn Point, Skaneateles Lake, N. Y. 

 Eroded shale (a) below, followed by fan or wedge-shaped reef-margin deposits 

 (6), with thinly, bedded shale (c) at the top. 



Plate XI. — Reef and reef -margin deposits near Staghorn Point, Skaneateles 

 Lake, N. Y. 

 Fig. 1. — Coral layers fanning away from the northern margin of the Southern 



